from __future__ import unicode_literals

import datetime
import os
import subprocess


def get_version(version=None):
    "Returns a PEP 386-compliant version number from VERSION."
    version = get_complete_version(version)

    # Now build the two parts of the version number:
    # major = X.Y[.Z]
    # sub = .devN - for pre-alpha releases
    #     | {a|b|c}N - for alpha, beta and rc releases

    major = get_major_version(version)

    sub = ''
    if version[3] == 'alpha' and version[4] == 0:
        git_changeset = get_git_changeset()
        if git_changeset:
            sub = '.dev%s' % git_changeset

    elif version[3] != 'final':
        mapping = {'alpha': 'a', 'beta': 'b', 'rc': 'c'}
        sub = mapping[version[3]] + str(version[4])

    return str(major + sub)


def get_major_version(version=None):
    "Returns major version from VERSION."
    version = get_complete_version(version)
    parts = 2 if version[2] == 0 else 3
    major = '.'.join(str(x) for x in version[:parts])
    return major


def get_complete_version(version=None):
    """Returns a tuple of the django version. If version argument is non-empy,
    then checks for correctness of the tuple provided.
    """
    if version is None:
        from django import VERSION as version
    else:
        assert len(version) == 5
        assert version[3] in ('alpha', 'beta', 'rc', 'final')

    return version


def get_git_changeset():
    """Returns a numeric identifier of the latest git changeset.

    The result is the UTC timestamp of the changeset in YYYYMMDDHHMMSS format.
    This value isn't guaranteed to be unique, but collisions are very unlikely,
    so it's sufficient for generating the development version numbers.
    """
    # FIXME: Replace with @lru_cache when we upgrade the docs server to PY2.7+.
    if hasattr(get_git_changeset, 'cache'):
        return get_git_changeset.cache

    repo_dir = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
    git_log = subprocess.Popen('git log --pretty=format:%ct --quiet -1 HEAD',
            stdout=subprocess.PIPE, stderr=subprocess.PIPE,
            shell=True, cwd=repo_dir, universal_newlines=True)
    timestamp = git_log.communicate()[0]
    try:
        timestamp = datetime.datetime.utcfromtimestamp(int(timestamp))
    except ValueError:
        changeset = None
    else:
        changeset = timestamp.strftime('%Y%m%d%H%M%S')

    get_git_changeset.cache = changeset
    return changeset
